The present invention relates to horology and more particularly to an electro-optical device which displays the time.
At the present time, the most common types of watches are mechanical and electro-mechanical. The mechanical watches are powered by a spring which is either wound up by an external knob, or by the swinging of weights in an "automatic" watch. The spring operates a time standard, which is generally a balance wheel. The oscillatory motion of the balance wheel controls the rotary motion of a series of gears which rotate hands. The hands, usually a second hand, minutes hand and hour hand, move clockwise over the dial and beneath the protective transparent crystal to indicate time by means of cooperation with numerals or other markings on the face of the dial.
In the electro-mechanical watches the power source is an internal battery which powers a small motor, for example, a tuning fork type of motor or a balance wheel type of motor, which rotates the time display hands. Watches are also available in which the motor is synchronized by means of a quartz crystal oscillator circuit to obtain a higher accuracy.
Watches are also available, although at a relatively higher price, in which a quartz crystal oscillator is used as the time standard and the high frequency of the oscillator is reduced by means of a series of countdown circuits. The count-down circuits operate a display driver which is connected to an electro-optical display. The electro-optical display may be of the liquid crystal type in which segments are selectively activated by the display driver to form digital numbers. Although some consumers prefer a digital numerical type of display, many others, who are familiar with the rotation of hands, prefer to tell time by the position of two or three hands as they move clockwise in relationship to a dial, this latter type of display sometimes being called an "analog display".
One major problem which has been encountered in developing such an analog type of electro-optical time display has been that of leakage currents. Such leakage currents arise from the voltage applied to the activated segments. The leakage currents between the activated segments may be sufficient to activate other, i.e., unwanted, segments. This may give an incorrect time reading, may be annoying, and may waste power. The life of the battery cell and the liquid crystal material may be reduced because of such leakage currents.
Typical of the prior art are U.S. Pat. No. 3,776,615 to M. Tsukamoto which issued Dec. 4, 1973, and No. 3,789,388 to A. H. Medwin which issued Jan. 29, 1974.
It is an objective of the present invention to provide a liquid crystal electro-optical display for a horological movement in which the appearance will be similar to that of the movement of two or three hands, for example, the seconds, minutes and hour hands, as they rotate clockwise in relationship to a center, thereby simulating the appearance of hands in conventional mechanical watches.
It is a further objective of the present invention to provide such an electro-optical display that is relatively simple in construction, relatively low in initial cost, has little likelihood of failure in use, and which is accurate because only the desired segments are activated.
It is still a further objective of the present invention that such an electro-optical display use relatively little power, so that the life of the battery cell within the watch case may be prolonged.